心磷脂重构酶ALCAT1调节线粒体功能和肝脏脂质代谢的机制研究

Oxidative stress causes mitochondrial dysfunction, which is implicated in the etiology of nonalcoholic fatty liver disease (NAFLD). However, the molecular mechanisms underlying the pathogenesis remain poorly elucidated. We recently identified a novel pathway by which oxidative stress causes mitochondrial dysfunction in metabolic diseases. This pathway is mediated by ALCAT1, a cardiolipin (CL) remodeling enzyme. Our work shows that ALCAT1 catalyzes the pathological remodeling of CL with fatty acyl chains that are highly sensitive to lipid peroxidation, leading to CL depletion and mitochondrial dysfunction. In support of a key role of the enzyme in mitochondrial etiology of age-related metabolic diseases, ALCAT1 expression is induced by ROS in obesity, triggering a vicious cycle of oxidative stress, CL peroxidation, and mitochondrial dysfunction. Consequently, ablation of ALCAT1 in mice prevents the onset of diet-induced obesity (DIO), type 2 diabetes, and cardiovascular disease. Additionally, ALCAT1 deficiency significantly improves the mitochondrial quality control process by abrogating defective mitochondrial fusion and autophagy, two common defects associated with obesity. Strikingly, our preliminary data also demonstrate that ALCAT1 deficiency prevents the onset of obesity-induced NAFLD. These data have led us to hypothesize that up-regulated ALCAT1 expression by obesity causes NAFLD by impairing mitochondrial fusion and autophagy.

心磷脂位于线粒体内膜上，通过调节内膜电子转运影响线粒体的功能。我们首先发现了心磷脂重构酶ALCAT1，并建立了ALCAT1全身敲除小鼠模型。该小鼠模型高脂喂养后肝脏脂质沉积减少、肝细胞线粒体损伤减轻，提示ALCAT1对小鼠肝脏组织脂质代谢及线粒体功能发挥重要的调节作用。本课题拟建立ALCAT1肝细胞特异性敲除小鼠模型，进一步明确ALCAT1在肝细胞脂质代谢和线粒体功能方面发挥的生理功能。我们的研究证实ALCAT1通过调节线粒体融合蛋白MFN2影响线粒体功能。我们拟建立MFN2/ALCAT1双基因肝细胞特异性敲除小鼠模型，分析其肝脏脂质代谢及线粒体功能，解析ALCAT1在肝脏组织中调节脂质代谢及线粒体功能的作用机制，揭示ALCAT1在脂肪肝发病中的病理学意义，从而为NAFLD的防治提供新的理论基础。

自噬障碍参与了非酒精性脂肪肝病的发病，但目前机制不明。心磷脂是一种线粒体磷脂，从酵母到哺乳动物线粒体自噬所必需的。通过项目的资助，我们主要研究了ALCAT1在非酒精性脂肪肝病发病中的作用。ALCAT1是一种溶血心磷脂酰基转移酶，在衰老相关疾病中可以催化病理条件下心磷脂的重构。我们研究发现，饮食诱导的非酒精性脂肪肝中肝细胞自噬受到限制，导致了氧化应激，线粒体功能损伤并且产生了胰岛素抵抗。在小鼠非酒精性脂肪肝病小鼠模型中，我们发现肝脏ALCAT1的表达明显升高。为了进一步研究ALCAT1的生理功能，我们构建了ALCAT1全身敲除小鼠，对小鼠进行高脂喂养后对表型进行了深入的分析和研究。研究结果表明，高脂喂养的ALCAT1敲除小鼠在线粒体自噬、线粒体结构和氧化磷酸化等方面均比对照小鼠得到了明显改善。同时，我们分离了小鼠原代肝细胞并过表达ALCAT1，发现过表达ALCAT1的原代肝细胞表现出脂肪变性，自噬缺陷和线粒体功能受损，进一步说明了ALCAT1介导的病理性心磷脂重构在非酒精性脂肪肝病的发病中发挥着重要的作用。